In the field of magnetic tape, with the prevalence of the office computer, such as minicomputers, personal computers and work stations, magnetic tapes for recording computer data as external storage media (a so-called backup tape) have been eagerly studied. In putting magnetic tapes for such uses to practical use, the improvement of recording capacity has been strongly demanded conjointly with the miniaturization of a computer and the increase of throughput for achieving high capacity recording and the miniaturization.
Magnetic recording media comprising a support having coated thereon a magnetic layer comprising an iron oxide, a Co-modified iron oxide, CrO2, ferromagnetic metal powder, or hexagonal ferrite powder dispersed in a binder have been conventionally widely used. Of these powders, ferromagnetic alloy powders of fine particles and hexagonal ferrite fine powders are known to be excellent in high density recording characteristics. However, when inductive heads which have been mainly used in the system using flexible media are used, these ferromagnetic powders are small in saturation magnetization, hence sufficient output cannot be obtained. However, a magneto-resistance head (an MR head) which is used in a hard disc has also come to be used in removable recording using flexible media as above.
Since an MR head is high sensitivity and capable of obtaining sufficient reproduction output, when magnetic fine particles having relatively low saturation magnetization as is used, a high C/N ratio can be obtained by the reduction of noise. For instance, an example of the reproduction with an MR head by using a barium ferrite (BaFe) fine particles is disclosed in JP-A-10-302243 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”).
In a recording system of high recording density (in particular, track recording density), it is necessary to optimize the relationship between recording conditions and the medium, besides an MR head is used at reproduction. In high track recording density, the gap of recording heads is generally made small for reducing the influences such as recording demagnetization and bit shift at recording, by which, however, recording magnetic field narrows and overwriting and thickness loss are traded off. Further, since the width of magnetic flux revolution narrows, the influence of turbulence of magnetization in a magnetization transition region cannot be negligible, which results in the loss of S/N ratio.
Further, it is discussed to obtain a high C/N ratio by using ferromagnetic metal powders, but the noise near the carrier increases when ferromagnetic metal powders are used as compared with the time when a metal evaporation tape (hereinafter referred to as an ME tape) is used, and so the reduction of the noise near the carrier is desired.
Further, the reliability of the time when data are repeatedly used and saved is also required of a magnetic recording medium. Accordingly, a magnetic recording medium is demanded to have good running durability in addition to excellent electromagnetic characteristics. For that sake, particularly in tape media, the improvement of running durability is contrived by providing a backing layer. To improve running durability by a backing layer, providing protrusions on the support surface, or roughening the surface of a backing layer by adding coarse particle carbon having a particle size of 0.1 μm or more has been tried. However, if the surface of a backing layer is roughened by these methods, when a magnetic recording tape is wound onto a hub for preservation or processing, the backing layer and the magnetic layer are tightly pressed and the protrusions of the backing layer are impressed on the magnetic layer, i.e., so-called “setoff”, is caused. As a result, a drawback such that electromagnetic characteristics are deteriorated arises. For solving such “setoff”, it is tried to smooth the backing layer surface.
As an example of the trial of smoothing a backing layer for improving the setoff to thereby increase electromagnetic characteristics, an example of using a mixture of granular titanium oxide and carbon black as a main ingredient is disclosed in JP-A-11-259851.
However, as described above, further reduction of the noise near the carrier and the security of running durability are desired.